This application is for the further investigation of the causes, pathogenesis and ultrastructure of pigment-producing and related ocular tumors. The new investigations will utilize knowledge gained from work carried out during a seven-year period under NEI Grant EY-00108 and EY 01917-01 and EY 01917-02. The continuation proposal represents a continuation of several basic aspects of the previous study and the initiation of related studies: 1. A histopathologic study of the changes occurring when normal ocular tissues become malignant. 2. Investigation of the possible role of viruses in the development of intraocular tumors, as determined by ultrastructural and biochemical studies. 3. Specific morphologic and biochemical changes resulting from malignant transformation by RNA and DNA oncogenic viruses and a comparison of these induced changes to the findings in spontaneous human ocular tumors.